Inter-channel crosstalk phenomena in optical time division multiplexed switching networks

The nature of inter-channel crosstalk arising in OTDM switching networks formed from imperfectly isolated 2/spl times/2 crosspoints and optical delay lines is investigated and a novel classification is identified. It is shown that the mixing of crosstalk and signal waveforms which are either, a) mutually coherent or, b) incoherent and (optical) frequency matched to within the receiver bandwidth, may result in intensity noise and far greater performance degradation than for c) incoherent signals whose optical beat frequency exceeds the receiver bandwidth. Initial experimental studies indicate that crosspoint isolation <-15 dB is required if undilated networks containing more than four crosspoints are to be realised.<>